The invention relates to an electrosurgical device, in the form of a catheter, and instrumentation for use in performing tissue ablation.
The ablation of organ tissue can be performed during surgical procedures to treat disease or medical disorders. Ablation of certain cardiac tissue is performed with increasing frequency to treat certain heart disorders which result in arrhythmia.
The heart is a muscular organ comprising four separate chambers which cooperate to pump blood throughout the body. The heart muscles must contract and relax in a coordinated sequence in order for blood to be passed through the circulatory system in an efficient manner. The heart includes a specialized system for generating impulses to cause rhythmical contraction of the heart muscle and for conducting these impulses rapidly through the heart. In the proper sequence the atria contract about one sixth of a second prior to the ventricles. This enables extra filling of the ventricles before they contract to pump blood through the lungs and to other areas of the body.
The basic timing impulse of the heart is generated in the sinoatrial node (SA node). The SA node has an inherent rhythm which can be modified by the sympathetic and parasympathetic nervous system. The impulse initiated by the SA node spreads through the atrium to the atrio-ventricular node (AV node), and then through the Purkinje fibers to the endocardial surfaces of the ventricles.
The rhythmical and conduction system of the heart is susceptible to disruption by disease. Damage caused to cardiac tissue can result in the inability of the cardiac conduction pathways to properly transmit the electrical impulses generated in the SA node, leading to arrhythmias, or irregular heartbeats. Cardiac arrhythmias can often be detected through electrocardiograms.
Some forms of cardiac arrhythmia are able to be controlled through medication. However, other forms of arrhythmia do not respond to medication. Moreover, medication typically does not cure the problem, and the dosage and the medication type must be changed periodically to maintain a continued level of control of the problem.
One alternative to medication is the surgical removal of a portion of the cardiac pathway which is responsible for the arrhythmia. The many dangers associated with open heart surgery render this a less preferred treatment option. Recently, however, it has become possible to intravascularly insert a specialized catheter within the heart, for positioning adjacent to the conductive tissue responsible for the arrhythmia. The catheter is adapted to deliver energy (e.g., radio frequency energy) to ablate or destroy the tissue lesion responsible for an arrhythmia. This has been found to be a relatively safe and effective technique for eliminating many causes of arrhythmia. Various ablation catheters and techniques for their use are described in U.S. Pat. Nos. 4,641,649; 4,785,815; 4,869,248; and 4,896,671.
Cardiac ablation catheters typically have at least one ablation electrode, positioned at the distal end of the catheter, which is adapted to deliver energy to the tissue lesion. Other electrodes can be proximally positioned on the catheter and used for sensing endocardial signals. Ablation may be achieved by the application of electrical energy, such as radio frequency (RF) or direct current (DC) energy, from a generator source, through a conductor disposed within the catheter, and to the ablation electrode.
During the ablation procedure, the ablation electrode is positioned adjacent to an ablation site, or site of defective tissue. The processes for accurately positioning the ablation electrode and "mapping" the ablation site are well known, and generally involve positioning a multi-electrode "mapping catheter," which may include an ablation tip, near the lesion, and radiographically visualizing the catheter position while simultaneously electrically monitoring the heart tissue. Once the ablation electrode is accurately positioned, energy, typically in the form of RF energy, is delivered to the ablation site by the ablation electrode.
The goal of the ablation procedure is to precisely destroy the defective tissue without damaging any healthy heart tissue. To prevent inadvertent damage of healthy tissue, it is desirable to monitor both the endocardial signal and the impedance at the ablation site during the ablation procedure. Monitoring is normally performed by one or more sensing electrodes proximally positioned on the catheter some distance away from the ablation electrode. Thus, in prior ablation systems, monitoring is not performed directly at the ablation site. This spatial discrepancy can result in an imprecisely controlled ablation procedure which may damage some healthy tissue, or fail to remove some of the defective tissue.
It would thus be advantageous to develop an ablation catheter system, suitable for use in cardiac ablation procedures, which measures the local impedance and the local endocardial signal directly at the ablation site. It would also be advantageous to develop a system that performs these measurements simultaneously with ablation.